Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system and the leading cause of a progressive dementia in the elderly population. Its clinical symptoms are impairment of memory, cognition, temporal and local orientation, judgment and reasoning but also severe emotional disturbances. There are currently no treatments available which can prevent the disease or its progression or stably reverse its clinical symptoms. AD has become a major health problem in all societies with high life expectancies and also a significant economic burden for their health systems.
AD is characterized by two major pathologies in the central nervous system (CNS), the occurrence of amyloid plaques and neurofibrillar tangles (Hardy et al., The amyloid hypothesis of Alzheimer's disease: progress and problems on the road to therapeutics, Science. Jul. 19, 2002; 297(5580):353-6, Selkoe, Cell biology of the amyloid beta-protein precursor and the mechanism of Alzheimer's disease, Annu Rev Cell Biol. 1994; 10:373-403). Both pathologies are also commonly observed in patients with Down's syndrome (trisomy 21), which also develop AD-like symptoms in early life. Neurofibrillar tangles are intracellular aggregates of the microtubule-associated protein tau (MAPT). Amyloid plaques occur in the extracellular space; their principal components are Aβ-peptides. The latter are a group of proteolytic fragments derived from the β-amyloid precursor protein (APP) by a series of proteolytic cleavage steps. Several forms of APP have been identified of which the most abundant are proteins of 695, 751 and 770 amino acids length. They all arise from a single gene through differential splicing. The Aβ-peptides are derived from the same domain of the APP but differ at their N- and C-termini, the main species are of 40 and 42 amino-acid length. There are several lines of evidence which strongly suggest that aggregated Aβ-peptides are the essential molecules in the pathogenesis of AD: 1) amyloid plaques formed of Aβ-peptides are invariably part of the AD pathology; 2) Aβ-peptides are toxic for neurons; 3) in Familial Alzheimer's Disease (FAD) the mutations in the disease genes APP, PSN1, PSN2 lead to increased levels of Aβ-peptides and early brain amyloidosis; 4) transgenic mice which express such FAD genes develop a pathology which bears many resemblances to the human disease. Aβ-peptides are produced from APP through the sequential action of 2 proteolytic enzymes termed β- and γ-secretase. β-Secretase cleaves first in the extracellular domain of APP approximately 28 amino acids outside of the trans-membrane domain (TM) to produce a C-terminal fragment of APP containing the TM- and the cytoplasmatic domain (CTFβ). CTFβ is the substrate for γ-secretase which cleaves at several adjacent positions within the TM to produce the Aβ peptides and the cytoplasmic fragment. The γ-secretase is a complex of at least four different proteins, its catalytic subunit is very likely a presenilin protein (PSEN1, PSEN2). The β-secretase (BACE1, Asp2; BACE stands for β-site APP-cleaving enzyme) is an aspartyl protease which is anchored into the membrane by a transmembrane domain (Vassar et al., Beta-secretase cleavage of Alzheimer's amyloid precursor protein by the transmembrane aspartic protease BACE, Science. Oct. 22, 1999; 286(5440): 735). It is expressed in many tissues of the human organism but its level is especially high in the CNS. Genetic ablation of the BACE1 gene in mice has clearly shown that its activity is essential for the processing of APP which leads to the generation of Aβ-peptides, in the absence of BACE1 no Aβ-peptides are produced (Luo et al., Mice deficient in BACE1, the Alzheimer's beta-secretase, have normal phenotype and abolished beta-amyloid generation, Nat Neurosci. March 2001; 4(3):231-2, Roberds et al., BACE knockout mice are healthy despite lacking the primary beta-secretase activity in brain: implications for Alzheimer's disease therapeutics, Hum Mol Genet. Jun. 1, 2001; 10(12):1317-24). Mice which have been genetically engineered to express the human APP gene and which form extensive amyloid plaques and Alzheimer's disease like pathologies during aging fail to do so when β-secretase activity is reduced by genetic ablation of one of the BACE1 alleles (McConlogue et al., Partial reduction of BACE1 has dramatic effects on Alzheimer plaque and synaptic pathology in APP Transgenic Mice. J Biol Chem. Sep. 7, 2007; 282(36):26326). It is thus presumed that inhibitors of BACE1 activity can be useful agents for therapeutic intervention in AD.
Type 2 diabetes (T2D) is caused by insulin resistance and inadequate insulin secretion from pancreatic β-cells leading to poor blood-glucose control and hyperglycemia (M Prentki & C J Nolan, “Islet beta-cell failure in type 2 diabetes.” J. Clin. Investig. 2006, 116(7), 1802-1812). Patients with T2D have an increased risk of microvascular and macrovascular disease and a range of related complications including diabetic nephropathy, retinopathy and cardiovascular disease. In 2000, an estimated 171 million people had the condition with the expectation that this figure will double by 2030 (S Wild, G Roglic, A Green, R. Sicree & H King, “Global prevalence of diabetes”, Diabetes Care 2004, 27(5), 1047-1053), making the disease a major healthcare problem. The rise in prevalence of T2D is associated with an increasingly sedentary lifestyle and high-energy food intake of the world's population (P Zimmet, KGMM Alberti & J Shaw, “Global and societal implications of the diabetes epidemic” Nature 2001, 414, 782-787).
β-Cell failure and consequent dramatic decline in insulin secretion and hyperglycemia marks the onset of T2D. Most current treatments do not prevent the loss of β-cell mass characterizing overt T2D. However, recent developments with GLP-1 analogues, gastrin and other agents show that preservation and proliferation of β-cells is possible to achieve, leading to an improved glucose tolerance and slower progression to overt T2D (L L Baggio & D J Drucker, “Therapeutic approaches to preserve islet mass in type 2 diabetes”, Annu Rev. Med. 2006, 57, 265-281).
Tmem27 has been identified as a protein promoting beta-cell proliferation (P Akpinar, S Kuwajima, J Krützfeldt, M Stoffel, “Tmem27: A cleaved and shed plasma membrane protein that stimulates pancreatic β cell proliferation”, Cell Metab. 2005, 2, 385-397) and insulin secretion (K Fukui, Q Yang, Y Cao, N Takahashi et al., “The HNF-1 target Collectrin controls insulin exocytosis by SNARE complex formation”, Cell Metab. 2005, 2, 373-384). Tmem27 is a 42 kDa membrane glycoprotein which is constitutively shed from the surface of β-cells, resulting from a degradation of the full-length cellular Tmem27. Overexpression of Tmem27 in a transgenic mouse increases β-cell mass and improves glucose tolerance in a diet-induced obesity DIO model of diabetes. Furthermore, siRNA knockout of Tmem27 in a rodent β-cell proliferation assay (e.g. using INS1e cells) reduces the proliferation rate, indicating a role for Tmem27 in control of β-cell mass.
In the same proliferation assay, BACE2 inhibitors also increase proliferation. However, BACE2 inhibition combined with Tmem27 siRNA knockdown results in low proliferation rates. Therefore, it is concluded that BACE2 is the protease responsible for the degradation of Tmem27. Furthermore, in vitro, BACE2 cleaves a peptide based on the sequence of Tmem27. The closely related protease BACE1 does not cleave this peptide and selective inhibition of BACE1 alone does not enhance proliferation of β-cells.
The close homolog BACE2 is a membrane-bound aspartyl protease and is co-localized with Tmem27 in human pancreatic β-cells (G Finzi, F Franzi, C Placidi, F Acquati et al., “BACE2 is stored in secretory granules of mouse and rat pancreatic beta cells”, Ultrastruct Pathol. 2008, 32(6), 246-251). It is also known to be capable of degrading APP (I Hussain, D Powell, D Howlett, G Chapman et al., “ASP1 (BACE2) cleaves the amyloid precursor protein at the β-secretase site” Mol Cell Neurosci. 2000, 16, 609-619), IL-1R2 (P Kuhn, E Marjaux, A Imhof, B De Strooper et al., “Regulated intramembrane proteolysis of the interleukin-1 receptor II by alpha-, beta-, and gamma-secretase” J. Biol. Chem. 2007, 282(16), 11982-11995) and ACE2. The capability to degrade ACE2 indicates a possible role of BACE2 in the control of hypertension.
Inhibition of BACE2 is therefore proposed as a treatment for T2D with the potential to preserve and restore β-cell mass and stimulate insulin secretion in pre-diabetic and diabetic patients Inhibitors of BACE1 and/or BACE2 can in addition be used to treat the following diseases: IBM (inclusion body myositis) (Vattemi G. et al., Lancet. Dec. 8, 2001; 358(9297):1962-4), Down's Syndrome (Barbiero L. et al, Exp Neurol. August 2003; 182(2):335-45), Wilson's Disease (Sugimoto I. et al., J Biol Chem. Nov. 30, 2007; 282(48):34896-903), Whipple's disease (Desnues B. et al., Clin Vaccine Immunol. February 2006; 13(2):170-8), SpinoCerebellar Ataxia 1 and SpinoCerebellar Ataxia 7 (Gatchel J. R. et al., Proc Natl Acad Sci USA Jan. 29, 2008; 105(4):1291-6), Dermatomyositis (Greenberg S. A. et al., Ann Neurol. May 2005; 57(5):664-78 and Greenberg S. A. et al., Neurol May 2005; 57(5):664-78), Kaposi Sarcoma (Lagos D. et al, Blood, Feb. 15, 2007; 109(4):1550-8), Glioblastoma multiforme (E-MEXP-2576, http://www.ebi.ac.uk/microarray-as/aer/result?queryFor=PhysicalArrayDesign&aAccession=A-MEXP-258), Rheumatoid arthritis (Ungethuem U. et al, GSE2053), Amyotrophic lateral sclerosis (Koistinen H. et al., Muscle Nerve. October 2006; 34(4):444-50 and Li Q. X. et al, Aging Cell. April 2006; 5(2):153-65), Huntington's Disease (Kim Y. J. et al., Neurobiol Dis. May 2006; 22(2):346-56. Epub Jan. 19, 2006 and Hodges A. et al., Hum Mol Genet. Mar. 15, 2006; 15(6):965-77. Epub Feb. 8, 2006), Multiple Mieloma (Kihara Y. et al, Proc Natl Acad Sci USA. Dec. 22, 2009; 106(51):21807-12), Malignant melanoma (Talantov D. et al, Clin Cancer Res. Oct. 15, 2005; 11(20):7234-42), Sjogren syndrome (Basset C. et al., Scand J Immunol. March 2000; 51(3):307-11), Lupus erythematosus (Grewal P. K. et al, Mol Cell Biol. July 2006; 26(13):4970-81), Macrophagic myofasciitis, juvenile idiopathic arthritis, granulomatous arthritis, Breast cancer (Hedlund M. et al, Cancer Res. Jan. 15, 2008; 68(2):388-94 and Kondoh K. et al., Breast Cancer Res Treat. March 2003; 78(1):37-44), Gastrointestinal diseases (Hoffmeister A. et al, JOP. Sep. 4, 2009; 10(5):501-6), Autoimmune/inflammatory diseases (Woodard-Grice A. V. et al., J Biol Chem. Sep. 26, 2008; 283(39):26364-73. Epub Jul. 23, 2008), Rheumatoid Arthritis (Toegel S. et al, Osteoarthritis Cartilage. February 2010; 18(2):240-8. Epub Sep. 22, 2009), Inflammatory reactions (Lichtenthaler S. F. et al., J Biol Chem. Dec. 5, 2003; 278(49):48713-9. Epub Sep. 24, 2003), Arterial Thrombosis (Merten M. et al., Z Kardiol. November 2004; 93(11):855-63), Cardiovascular diseases such as Myocardial infarction and stroke (Maugeri N. et al., Srp Arh Celok Lek. January 2010; 138 Suppl 1:50-2) and Graves disease (Kiljański J. et al, Thyroid. July 2005; 15(7):645-52).